1. Field of the Invention
The invention relates to shut-off pipeline fittings, and more specifically, it deals with a gate valve.
2. Description of the Prior Art
A gate valve according to the invention may be most efficiently used in pipelines intended for conveying suspended abrasive materials, preferably slurries.
The invention may be used in the mining, construction and chemical industries and also in other industries employing hydraulic and pneumatic conveyance of fluids in the form of suspensions and slurries containing solid particles, especially of fluids which cause a highly intensive wear of the seat and gate which should be replaced during operation.
Known in the art is a gate valve, comprising a casing having a passage. A gate is accommodated in the casing and a seat is installed in alighment with the centerline of the passage (cf. USSR Inventor's Certificate No. 450922, Cl. F 16 k 3/14, F 16 k 3/30, Nov. 25, 1974).
Two stops are installed transversely of the centerline of the passage, the stops engaging with their tapered surfaces tapered faces of the gate provided on the gate side opposite to the side thereof facing toward the seat, when the gate is in the closed position.
The stops are disposed so that each stop is located on the side of the gate opposite to the side thereof facing toward the seat, and adjacent to the side surfaces at the level of the passage centerline.
The tapered surfaces are provided on the side of the gate opposite to the side thereof facing toward the seat and make an acute angle with the direction of movement of the gate into its shut-off position.
When the stops engage the tapered surfaces of the gate, they urge the gate against the end face of the seat facing toward the gate thus ensuring the sealing when the passage is shut-off.
For tightly pressing the gate against said end face of the seat and for ensuring the tightly sealed shutting-off of the passage, the stops should accurately mate with said tapered surfaces.
In the prior art gate valve the stops are rigidly secured to the end face of rods accommodated in the casing. Each rod is installed in a hole of a casing wall along an axis extending transversely of the centerline of the passage for a limited rotation about its axis.
As a result of a rather rapid wear of said seat and gate during operation of the gate valve with abrasive slurries, the distance from the end face of the seat facing toward the cooperating surface to the surface of the stops engaging the tapered faces of the gate should be adjusted frequently.
In the prior art gate valve the end face portion of each rod facing toward the passage is made in the form of a step formed by cutting-off the cylindrical part of the rod to one-half of its diameter.
The stop is secured to the flat faces of the step facing toward the seat, and a set of thin spacers are installed between this surface of the step and the surface of the stop facing toward this surface.
By varying the number of the spacers and thickness of said set the distance from the surface of the seat facing toward the gate to the stop surfaces engaging the tapered faces of the gate may be adjusted.
The amount of rotation of each rod is determined by clearances between the end of a rigidly secured pin protruding from the casing and the wall of a groove made in the rod.
Owing to a limited rotation of the rods about their axes, the rods intimately engage said tapered faces of the gate with their surfaces engageable with the tapered faces of the gate thereby compensating for manufacturing tolerances of angles of taper.
When the prior art gate valve is used, the above-described adjustment of the distance from the surface of the seat facing toward the gate to the surfaces of the stops engageable with the tapered faces of the gate by varying the number of spaces and thickness of the set of spacers is difficult because the rods with the stops secured thereto must be withdrawn from the casing which is only possible after the disconnection of the pipeline thus impairing the cost-effectiveness.
In addition, thin spacers which are normally used in the stops have rather short service life because of corrosion, especially when the gate valves work with abrasive and aggressive fluids.